In the context of Cooperative Intelligent Transport Systems (C-ITS) applications, ETSI TS 103 084 V0.0.3 “Geomessaging Enabler” suggests to use a geographically targeted distribution mechanism referred to as Geomessaging (GM). As described in “An Optimized Grid-Based Geocasting Method for Cellular Mobile Networks” by G. Jodlauk et al., ITS World Congress 2011, Orlando, USA, October 2011, and in WO 2012/055433 A1, this concept involves a GM server which tracks the position of GM clients using a grid-based scheme. GM clients notify the GM server when they move to another field of the grid, which allows the GM server to continuously update a mapping of GM clients to grid areas. Based on this mapping, the GM server can serve distribution requests by different application servers and forward messages in nearly real-time to GM clients in a designated geographic area, which in turn provide the messages further to their associated application clients.
A further known way for implementing the above-mentioned C-ITS applications is to use ad-hoc networks, in particular a Wireless Local Area Network according to the IEEE 802.11p standard. Using such ad-hoc network, the C-ITS application in a vehicle may communicate directly with the C-ITS application in another vehicle, without requiring usage of a centralized C-ITS server. When using an ad-hoc network for implementing C-ITS applications geographic targeting of message distribution is typically inherent, because only receivers within limited range from the sender will be able to receive messages from the sender. On the other hand, usage of cellular communication for C-ITS applications allows for covering larger areas and does not require dedicated road side infrastructure, but typically requires additional infrastructure to support targeting of selected geographical areas, such as the above-mentioned GM mechanism.
Further, in “Geocasting over 11p, LTE and beyond”, A. Festag, 4th ETSI TC ITS Workshop, February 2012, Doha, Quatar, also a hybrid system is suggested which combines both cellular communication using the LTE (Long Term Evolution) radio technology specified by 3GPP (3rd Generation Partnership Project) and ad-hoc network communication using the ITS-G5 radio technology. In this case, a vehicle station is connected to a server via the cellular LTE radio technology and may forward messages to or from other vehicle stations via the ad-hoc ITS-G5 radio technology. However, this hybrid system may have problems concerning the efficiency of message distribution over the cellular network. For example, to be sure that the vehicle stations connected over the ITS-G5 radio technology are provided with all relevant messages, all potentially relevant messages need to be provided to the vehicle station connected via the LTE radio technology. However, it may occur that some of these messages are actually not relevant for the vehicle stations and have been unnecessarily transmitted. This means that resources of the LTE radio technology are not efficiently utilized, which is undesirable from a cost perspective and from a network capacity perspective.
Accordingly, there is a need for techniques which allow for efficiently performing geographically targeted distribution of application service messages.